Fiber optic transceivers interface with optical fibers for transmitting light signals thereto, typically through a light-emitting diode (LED) or like device responsive to electrical excitation to output light pulses corresponding with digital signals providing the information for such excitation. Signal to noise ratio is relatively high in the transmitter and information loss is according a low probability matter.
The contrary is the case with the receiver of the transceiver, incoming signal levels in the incoming optical fiber being relatively low. Receiver design is accordingly more demanding than transmitter design.
Fiber optic receivers typically have three sections, the first being a light sensor interfacing directly with the fiber and comprised of a photodiode or the like, responsive to incident light to issue output electrical signals corresponding to such incident light. The second section is a pre-amplifier and the third section is a post-amplifier, the former issuing an analog output signal and the latter converting such analog signal into a digital signal suitable for use in associated digital circuitry.
Experience with current commercial pre-amplifier chips designed for use in fiber optic receivers establishes that they are highly susceptible to interference from spurious signals and to oscillation due to feedback from latter stages of the receiver, for example, the post-amplifier. Intelligence is of course lost during such preamplifier oscillations, an undesired situation even in the environment of sophisticated error-correction encoding of transmitted data.